The present invention relates to a method for detecting whether dissimilar metals are being welded together. More particularly, the invention relates to a method for detecting whether dissimilar metals are being welded together which uses the principles of thermocouples and thereby provides a simple, quick, inexpensive and accurate means of eliminating metal mix-up via welding.
In metal processing industries, metal coils are welded together during processing to save set-up time in wire drawing and to meet minimum finish coil weight requirements, among other reasons. Typically, the identities of the two coils to be joined are kept by tags or labels attached to the coils. Wrong materials, however, are sometimes joined together due to mislabeling or due to other human errors. The mistaken joining of dissimilar metals results in costly rejection by customers and possible products liability damage suits by consumers. Thus it is evident that a simple, quick, inexpensive and accurate means for eliminating metal mix-up via welding has long been needed and is most desirable in the metal processing industries.
Various methods for the identification of metals exist in the prior art, but none offers all the advantages of the present invention. For example, chemical analysis can provide identification of a metal but it is both time consuming and expensive. Thermoelectric devices do exist for metal identification. However, one device requires cutting up samples of the metals for testing them in an electric furnace versus known metal or alloy standards. Another device involves the measurement of thermal electromotive force (EMF) of the unknown metal versus a copper beryllium alloy probe at about 350.degree. F., a temperature sometimes too low for distinguishing the difference between metals having similar EMF's at 350.degree. F. or below. Clearly the prior art does not provide a simple, quick, inexpensive and accurate means for eliminating metal mix-up.
It was recognized by the inventors that a weld joint is indeed the thermocouple bead, or hot junction, of a thermocouple. By using the Thermoelectric Law of Intermediate Metals as cited in Perry's Chemical Engineers' Handbook, 4th Ed., N.Y. McGraw-Hill Book Co., 1963, p. 22-6, which states:
"If in any circuit of solid conductors the temperature is uniform from any point P through all the conducting matter to a point Q, the algebraic sum of the thermoelectromotive forces in the entire circuit is totally independent of this intermediate matter and is the same as if P and Q were put into contact.";
the inventors recognized that the electrical connection of the metals at a point remote from the weld which is at substantially ambient temperature could act as the cold junction. Thus, if the metals to be joined together are of different materials, an EMF will develop. This EMF and the resulting thermoelectric current can be detected readily by a properly connected multipurpose potentiometer, an ammeter, or a voltmeter. However, if the metals to be joined are of identical materials, no EMF will be created as the Thermoelectric Law of the Homogeneous Circuit requires that an electric current cannot be sustained in a circuit of a single homogeneous metal, however varying in section, by the application of heat alone.
A quick and inexpensive method for detecting whether dissimilar metals are being welded together is provided, and includes the steps of welding the metals together, and contacting each metals at point heat conductively remote from the weld with electrical leads connected to a potentiometer. This arrangement forms a thermocouple with the weld bead as the hot junction, and the remote contact points at substantially ambient temperature as the cold junction. If the metals are dissimilar, an EMF and electrical current result and may be detected by the potentiometer. If the potentiometer indicates that no signal is generated, the welded metals are identical.
By a similar method using the same principles, an unknown metal may be positively identified. The unknown metal is welded to different known reference metals until no signal is generated.
It is therefore an object of this invention to provide a method for detecting whether dissimilar metals are being welded together, thereby eliminating costly rejections and products liability damage suits by the customers and ultimate consumers.
Another object of this invention is to provide a simple, quick, inexpensive and accurate method for eliminating metal mix-up via welding.
Another object of this invention is to detect whether dissimilar metals are being welded without having to cut the metals for testing.
Another object of this invention is to provide a method for the positive identification of an unknown metal.
These, and other objects and advantages of the invention will become more apparent from the detailed description and appended claims taken in conjunction with the accompanying drawings.